Experimental and analytical investigation of improved behavior of existing steel connections by adding self-centering capabilities

This study presents a new post-tensioning configuration for enhancing the seismic performance of existing steel bolted connections. The nonlinear behavior of the proposed post-tensioned connection was investigated through experimental and analytical programs. Different post-tensioning strand configurations were installed on top-and-seat angle connections with different strand length, strand number, and initial post-tensioning force. Data from the tested post-tensioned connections showed a significant improvement in the nonlinear behavior when compared to their non-post-tensioned counterparts. This improvement was achieved by increasing the overall stiffness and strength in addition to providing self-centering capabilities that could limit the residual drifts for the retrofitted moment-resisting frames after a strong earthquake. An analytical representation of the proposed connection is presented and modified considering the effect of the strand relaxation. The derived analytical equation accurately represented the response of the post-tensioned beam-to-column connection in terms of the moment-rotation relationship and it could be used for the analysis and design of post-tensioned connections subjected to large deformations